Recently, communication processing systems where viewers each make a contract with the sender and where only the receivers given the special right are allowed to watch the programs have become desirable for pay TV systems that charge the viewers TV licence fees as well as for the protection of copyrights.
Accordingly, an object of the present invention is to provide a transmission system and a reception system that permit only the privileged viewers under contract with the sender for reception of pay TV broadcasting to watch the programs, and a communication processing system that integrates these apparatuses.
Another object of the present invention is to provide a transmission system and a reception system that are capable of recording, editing, and exchanging the contents of communications with a third party, and a communication processing system that integrates these apparatuses.
In recent years, as video and audio digital signal processing technology have made remarkable progress, more and more research effort has been directed worldwide toward systems that realize digital television broadcasting and the fusion of broadcasting and communication. In this movement, some of the most important techniques are video and audio compression techniques.
Major compression techniques are MPEG, JPEG, and H.261. The schemes proposed by ISO/IEC 1318-1 (Moving Picture Experts Group (ISO/IECJTC1/SC29/WG11)) are now under examination for worldwide standardization of broadcasting, communications, and storage media.
ISO/IEC 13818-1 has determined not only an image compression scheme but also a scheme for a section where the transmission side compresses the video and audio data items of programs separately, generates and multiplexes the bit streams, and broadcasts the multiplexed signal, and a scheme for a control section that enables reception of a specified program on the reception side.
With the advances in digital signal processing techniques, pay digital television broadcasting has been considered. One of the most important problems here is the technique for charging the viewers.
As a conventional technique for dealing with this problem, a scrambling scheme has been proposed which is characterized by generating random numbers without changing the code length in a compression layer complying with the MPEG standard. Since MPEG uses variable-length quantization techniques, however, it is very difficult to effect scrambling without changing the code length.
With this backdrop, Matsushita's Image Laboratory has proposed a scheme at a meeting of the Electronic Data Communication Society of Japan in December, 1992. The scheme is such that the entire quantization scale or the entire fixed-length code of the DCT direct-current component is multiplied by PN, whereas for a motion vector or a variable-length code of the DCT alternating-current component, the codes in the code book are multiplied by PN.
With this scheme, when the compression-decoded images without descrambling are viewed, the contents of the images can hardly be understood, so that pay broadcasting can be realized by delivering descrambling units to the subscribers who have paid charges.
This scheme, however, has a disadvantages in that encoding and decoding are very difficult. Additionally, because the contents of programs cannot be understood without descrambling, it is difficult to let viewers other than the subscribers know the good points of the contents of programs.
If the resolution can be lowered to the extent that the contents of a program can be understood, it is possible to allow the program to appeal to would-be subscribers and motivate them to subscribe to the service. The above scheme with which would-be subscribers cannot recognize the contents of programs, however, can be considered to be unsuitable for practical broadcasting services.
As described above, in a digital television broadcasting system, with the conventional scramble broadcasting scheme, not only are encoding and decoding very difficult, but also the contents of programs can hardly be understood when the compression-decoded images are viewed without descrambling in the case of pay TV service. As a result, it is difficult to appeal to would-be subscribers and therefore, they are not motivated to subscribe to the service.
Accordingly, an object of the present invention is to provide as an example of the communication processing system a digital television broadcasting system as an example of the communication processing system which, even when a scrambled program is selected and decoded without descrambling, enables the program to be viewed to the extent that the contents of the program can be understood.